(1) Field of the Invention
This invention relates to the chemical treatment of fibrous lignocellulose-containing material to produce a swelling of the fibers which is correlated with hydrolysis after exposed to gamma radiation.
(2) Description of the Prior Art
The Prior Art teaches that lignocellulosic plant materials consist essentially of about 70% carbohydrate and 30% lignin. Nearly 70% of the carbohydrate is cellulose, the remainder is hemi-cellulose. Thus, about one-half of the dry plant matter is cellulose. On hydrolysis cellulose yields glucose, which can be used for a variety of purposes, including the fermentation to alcohol. Because cellulose is not water-soluble and not readily available for nutrition of man the first step in any process utilizing sugar from cellulose is hydrolysis, or the solubilization of cellulose.
Because of the abundance and urgency of utilizing lignocellulose considerable effort has been made in the past to hydrolyze the cellulose (see report A. E. Humphrey in "Hydrolysis of Cellulose: Mechanisms of Enzymatic and Acid Hydrolysis," in advances in Chemistry Series 181 "The Hydrolysis of Cellulosic Materials to Useful Products", pp 25-53 (1979)). J. Saeman, in Industrial And Engineering Chemistry, Vol. 37, page 43 (1945) reported on the hydrolysis of cellulose by the use of acid. The sugar yield, however, was too low and the sugar produced in the hydrolysis was easily destroyed by the acid and the heat. The use of acid required special acid-resistant materials for the equipment and necessitated the recovery of the acid, both of which complicated the process and increased the costs. Thus, due to economic reasons, commercial practice of acid hydrolysis of cellulose is limited.
Lignocellulose can also be hydrolyzed by the enzyme cellulase. The U.S. Army Natick Research and Development Command and several universities and research institutes have developed processes by which various lignocellulosics are hydrolyzed (see "Enzymatic Saccharification of Cellulose in Semi- and Continuously Agitated Systems," by T. K. Ghose and J. A. Kostick, Advances in Chemistry Series 95: pp 415-446 (1969)). In these processes, unlike acid hydrolysis, the released sugars are not decomposed but the rate of cellulose hydrolysis is extremely slow and often extensive pretreatments are needed. Production of enzyme and glucose are too costly to warrant economical practice at the present time.
Other investigators indicate that lignocellulose can be liquified by thermo-chemical conversions. Sabri Ergun of the Lawrence Berkeley Laboratory, University of California, Berkeley, Calif., published a report entitled "Biomass Liquefaction Efforts in the United States," in February 1980. This process was further improved by Battelle Pacific Northwest Laboratories and Lawrence Berkeley Laboratory of the University of Berkeley, in California. According to this process, lignocellulosic materials are treated under carbon monoxide and high temperature (260.degree. to 360.degree. C.) and high pressure (100 to 250 lbs/sq. in.) and produced two barrels of oil per ton of dry lignocellulosic material. The process is essentially hydrogenation (also called deoxygenation), in which oxygen is abstracted from cellulose by carbon monoxide and steam. Because of uncertain economic and unsolved technical problems this process is still in the experimental stage.
J. F. Saeman, M. A. Millett, and E. J. Lawton, as reported in "Effect of High-Energy Cathode Rays on Cellulose," in Industrial and Engineering Chemistry, Vol. 44, pp 2848-2852 (1952), investigated the possibility of using high-energy cathode rays on cellulose hydrolysis. They found that in order to solubilize cellulose a dosage of 3.3.times.10.sup.8 rad was required, and this level was too high to be practical. Any dosage less than that would only cause depolymerization and decomposition of carbohydrate material to an extent correlated to the dosage.
W. J. Pigden, G. I. Prichard, and D. P. Heaney irradiated forage crops with high energy gamma source (2.7.times.10.sup.8 rads) and found the digestibility of mature forage material increased. This was reported in "Physical and Chemical Methods for Increasing the Available Energy Content of Forages," Proceedings of the Xth International Grassland Congress, Paper No. 11 (1966). There are many other reports on gamma irradiation of lignocellulosic materials. All indicated that irradiation could improve the digestibility of lignocellulosic material but the dosage would be too high to solubilize cellulose. Thus, solubilization of lignocellulosic material by irradiation has not been considered economically feasible, and the art has not advanced.